Life on Earth has a long, but also an extremely turbulent history. On more than one occasion, the majority of all species became extinct and an already highly developed biodiversity shrank to a minimum again, changing the course of evolution each time. The most extensive mass extinction took place about 252 million years ago. It marked the end of the Permian Epoch and the beginning of the Triassic Epoch. About three quarters of all land life and about 95 percent of life in the ocean disappeared within only a few thousand years.
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Source: Phys.org